Seminatrix Research Articles

NEW PREY ITEM IN THE DIET OF THE Orange-bellied swamp snake Tretanorhinus nigroluteus COPE, 1861 (DIPSADIDAE) IN THE SELVA LACANDONA, CHIAPAS, MEXICO

The orange-bellied swamp snake (Tretanorhinus nigroluteus) is considered a rare species in Mexico; there are few specific records of its presence in the country. They are known to feed on amphibians (anurans) and fish of different species (Families Gobidae and Poecilidae). We report the first record of freshwater snails (Pachychilus largillierti) as prey of T. nigroluteus.

Landscape-Scale Effects of Supra-Seasonal Drought on Semi-Aquatic Snake Assemblages

Climate change is predicted to alter the frequency and intensity of precipitation events, placing stress on freshwater aquatic ecosystems and their associated wildlife. Thus, understanding interspecific variation in drought sensitivity and the repeatability of those responses across heterogeneous landscapes is critical. Semi-aquatic snakes serve important roles within aquatic ecosystems and several species are threatened. Yet, little is known about the effects of drought on semi-aquatic snake populations or assemblages. We systematically trapped 20 isolated wetlands in South Carolina before (2006) and after (2013) a multi-year supra-seasonal drought to determine drought-induced shifts in occupancy and detection for five semi-aquatic snake species. Our results confirm that supra-seasonal drought differentially affects semi-aquatic snake species across landscape scales. Specifically, site occupancy decreased dramatically following drought for banded watersnakes (Nerodia fasciata) (0.95 to 0.69) and Florida green watersnakes (Nerodia floridana) (0.32 to 0.05), but was relatively unchanged for black swamp snakes (Seminatrix pygaea), mudsnakes (Farancia abacura) and glossy crayfish snakes (Regina rigida). Species lacking adaptations that make them resistant or resilient to drought may become locally extirpated if climate change projections are realized or landscapes are degraded or fragmented in ways that prevent drought recovery.

Ecological and methodological factors affecting detectability and population estimation in elusive species

AbstractAlthough mark‐recapture methods are among the most powerful tools for monitoring wildlife populations, the secretive nature of some species requires a comprehensive understanding of the factors that affect capture probability to maximize accuracy and precision of population parameter estimates (e.g., population size and survivorship). Here, we used aquatic snakes as a case study in applying rigorous mark‐recapture methods to estimate population parameters for secretive species. Specifically, we used intensive field sampling and robust design mark‐recapture analyses in Program MARK to test specific hypotheses about ecological and methodological factors influencing detectability of two species of secretive aquatic snakes, the banded watersnake (Nerodia fasciata), and the black swamp snake (Seminatrix pygaea). We constructed a candidate set of a priori mark‐recapture models incorporating various combinations of time‐ and sex‐varying capture and recapture probabilities, behavioral responses to traps (i.e., trap‐happiness or trap‐shyness), and temporary emigration, and we ranked models for each species using Akaike's Information Criterion. For both banded watersnakes and black swamp snakes we found strong support for time‐varying capture and recapture probabilities and strong trap‐happy responses, factors that can bias population estimation if not accommodated in the models. We also found evidence of sex‐dependent temporary emigration in black swamp snakes. Our study is among the first comprehensive assessments of factors affecting detectability in snakes and provides a framework for studies aimed at monitoring populations of other secretive species. © 2010 The Wildlife Society.

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). VII. spermatozoon morphology and evolutionary trends of sperm characters in snakes

This study investigates the evolution of snake spermatozoa within a phylogenetic context, with the addition of a new ultrastructural description from the spermatozoa of the Black Swamp Snake, Seminatrix pygaea. Overall the spermatozoon of S. pygaea is similar to that described for other squamates, whereas some characters such as the electron lucent space separating the cortex and medulla of the acrosome complex may be a unique feature of S. pygaea spermatozoa. This preliminary analysis of sperm evolution within Serpentes leads to the hypothesis that some sperm characters are more plastic than others. Incongruencies are found between the molecular and the morphological topologies utilized, and the phylogeny derived from a morphological data set recovers more unequivocal ancestral states of snake sperm structure. Characters such as the beginning of the fibrous sheath at mitochondrial tier one unite the Colubroidea, whereas characters such as the presence of an acrosome vesicle subdivision, absent vacuity subdivision, and round ⁄ oval mitochondria in transverse section unite all squamates. However, from this analysis it is evident that more taxa need to be studied and taxa with current data need to be more thoroughly investigated to make more conclusive remarks regarding the evolution of sperm structure within snakes.

Seasonal variation in terrestrial resource subsidies influences trophic niche width and overlap in two aquatic snake species: a stable isotope approach

Quantifying diet is essential for understanding the functional role of species with regard to energy processing, transfer, and storage within ecosystems. Recently, variance structure in the stable isotope composition of consumer tissues has been touted as a robust tool for quantifying trophic niche width, a task that has previously proven difficult due to bias in direct dietary analyses and difficulties in integrating diet composition over time. We used carbon and nitrogen stable isotope analyses to examine trophic niche width of two sympatric aquatic snakes, banded watersnakes Nerodia fasciata and black swamp snakes Seminatrix pygaea inhabiting an isolated wetland where seasonal migrations of amphibian prey cause dramatic shifts in resource availability. Specifically, we characterized snake and prey isotope compositions through time, space, and ontogeny and examined isotope values in relation to prey availability and snake diets assessed by gut content analysis. We determined that prey cluster into functional groups based on similarity of isotopic composition and seasonal availability. Isotope variance structure indicated that the trophic niche width of the banded watersnake was broader (more generalist) than that of the black swamp snake. Banded watersnakes also exhibited seasonal variation in isotope composition, suggesting seasonal diet shifts that track amphibian prey availability. Conversely, black swamp snakes exhibited little seasonal variation but displayed strong ontogenetic shifts in carbon and nitrogen isotope composition that closely paralleled ontogenetic shifts in their primary prey, paedomorphic mole salamanders Ambystoma talpoideum. Although niche dimensions are often treated as static, our results demonstrate that seasonal shifts in niche dimensions can lead to changes in niche overlap between sympatric species. Such short-term fluctuations in niche overlap can influence competitive interactions and consequently the composition and dynamics of communities and ecosystems.

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). VI. Anterior testicular ducts and their nomenclature

In this study, the anterior testicular ducts of the North American natricine snake Seminatrix pygaea are described using light and electron microscopy. From the seminiferous tubules, the rete testis passes into the epididymal sheath, a structure along the medial border of the testis heavily invested with collagen fibers. The rete testis consists of simple, nonciliated cuboidal epithelium (principal cells). The intratesticular ducts of the rete testis are narrow (50-70 microm) at their junction with the seminiferous tubules, widen (80-100 microm) as they extend extratesticularly, and divide into smaller branches as they anastomose with the next tubules, the ductuli efferentes. The ductuli efferentes are lined by simple cuboidal epithelium but possess nonciliated principal cells as well as ciliated cells. These are the only ducts in the male reproductive system with ciliated cells. The ductuli efferentes are narrow (25-45 microm), divide into numerous branches, and are highly convoluted. The ductus epididymis is the largest duct in diameter (240-330 microm), and the diameter widens and the epithelium thins posteriorly. The ductus epididymis is lined by nonciliated, columnar principal cells and basal cells. No regional differences in the ductus epididymis are apparent. Ultrastructural evidence suggests that all of the nonciliated principal cells in each of the anterior testicular ducts function in both absorption and secretion. Absorption occurs via small endocytic vesicles, some of which appear coated. Secretion is by a constitutive pathway in which small vesicles and a flocculent material are released via a merocrine process or through the formation of apocrine blebs. The secretory product is a glycoprotein. Overall, the characteristics of the anterior testicular ducts of this snake are concordant with those of other amniotes, and the traditional names used for snakes are changed to conform with those used for other sauropsids and mammals.

Drought survival and reproduction impose contrasting selection pressures on maximum body size and sexual size dimorphism in a snake, Seminatrix pygaea

The causes and consequences of body size and sexual size dimorphism (SSD) have been central questions in evolutionary ecology. Two, often opposing selective forces are suspected to act on body size in animals: survival selection and reproductive (fecundity and sexual) selection. We have recently identified a system where a small aquatic snake species (Seminatrix pygaea) is capable of surviving severe droughts by aestivating within dried, isolated wetlands. We tested the hypothesis that the lack of aquatic prey during severe droughts would impose significant survivorship pressures on S. pygaea, and that the largest individuals, particularly females, would be most adversely affected by resource limitation. Our findings suggest that both sexes experience selection against large body size during severe drought when prey resources are limited, as nearly all S. pygaea are absent from the largest size classes and maximum body size and SSD are dramatically reduced following drought. Conversely, strong positive correlations between maternal body size and reproductive success in S. pygaea suggest that females experience fecundity selection for large size during non-drought years. Collectively, our study emphasizes the dynamic interplay between selection pressures that act on body size and supports theoretical predictions about the relationship between body size and survivorship in ectotherms under conditions of resource limitation.

Empirical Tests of Biased Body Size Distributions in Aquatic Snake Captures

Abstract Ecologists often rely on a suite of demographic parameters—such as age structure, body size distributions, population density, and sex ratios—to understand life history patterns, population dynamics, and community structure of snakes. Unfortunately, in many cases little consideration is given to how sampling techniques may influence the outcome of demographic studies. Herein, we use a combination of field capture techniques, an extensive database of field-captured snakes, and laboratory and field experiments to evaluate how capture methods may influence demographic assessments of several North American semi-aquatic snake species, including Agkistrodon piscivorus, Farancia abacura, Nerodia fasciata, N. floridana, N. rhombifer, N. taxispilota, Regina rigida, Seminatrix pygaea, and Thamnophis sauritus. We found that commercially available aquatic funnel traps (i.e., minnow traps) generally yielded biased assessments of population demography, but that the nature and magnitude of these biases varied p...

Post-drought responses of semi-aquatic snakes inhabiting an isolated wetland: Insights on different strategies for persistence in a dynamic habitat

Most aquatic habitats are temporally dynamic, and selection has favored diverse strategies to persist in the face of fluctuating environmental conditions. Isolated wetlands in the southeastern United States harbor high diversities of aquatic and semi-aquatic organisms. However, drought may render these wetlands temporarily unsuitable for many species, sometimes for years at a time. We studied the movement patterns and demography of seven species of semi-aquatic snakes at Ellenton Bay, an isolated 10-ha freshwater wetland in the Upper Coastal Plain of South Carolina, following complete drying of the bay during a drought from 2000 to 2003. Behavioral and population responses varied markedly among species. Cottonmouths (Agkistrodon piscivorus) migrated to and from the wetland annually, fared well, and reproduced during the drought. Banded watersnakes (Nerodia fasciata) suffered a dramatic population decline and apparently did not reproduce, while eastern green watersnakes (N. floridand) were locally extirpated. Black swamp snakes (Seminatrix pygaea) aestivated within the wetland and were less affected by the drought than Nerodia. Interspecific differences in response to drought demonstrate that conservation measures may affect species differently and highlight the importance of terrestrial habitat around wetlands for semi-aquatic reptiles.

Income breeding allows an aquatic snake Seminatrix pygaea to reproduce normally following prolonged drought‐induced aestivation

1. Capital breeding is an ideal reproductive strategy for many ectotherms because it provides a disassociation between feeding and reproduction, a necessary requirement for animals that become anorexic during pregnancy. Among ectotherms, some viviparous snakes (e.g. Viperidae) exemplify the capital breeding strategy because many species (i) do not feed during pregnancy due to behavioural conflicts between reproduction and foraging, and (ii) take more than one season to accumulate sufficient energetic stores for reproduction. 2. Isolated wetlands often exhibit extreme annual fluctuations in environmental conditions with prolonged droughts periodically leaving wetlands completely dry and devoid of prey. Following droughts, however, wetlands can be extremely productive, rendering prey resources virtually unlimited for some species. 3. This study examines drought survival strategy and reproductive ecology of a small aquatic snake Seminatrix pygaea (Cope) in an isolated wetland. Seminatrix pygaea are atypical from most sympatric snake species in that (i) their small body size, reliance on aquatic prey, and high rates of evaporative water loss make them ill-suited to overland movement, and (ii) they may not be subject to costs typically associated with feeding during pregnancy. 4. We hypothesized that S. pygaea would survive periodic multiyear droughts by aestivating within the dried wetland, a survival strategy heretofore undocumented in snakes. Further, we hypothesized that if S. pygaea rely on 'typical' snake reproductive strategies of 'adaptive anorexia' and capital breeding, reproductive output would be reduced in the first wet year following drought. 5. By encircling a 10-ha wetland with a continuous drift fence before it refilled we were able to demonstrate that S. pygaea were present within the dried wetland prior to the onset of spring rains that refilled the wetland in 2003. Our results suggest that S. pygaea are capable of surviving multiyear droughts by aestivating within the dried wetland. 6. Despite having presumably depleted energy reserves during the drought, S. pygaea reproduced with the same frequency and fecundity during the first season following refilling of the wetland as in pre-drought years. 7. The ability of S. pygaea to rebound rapidly from the stresses of prolonged drought is due in part to their reproductive ecology. Seminatrix pygaea readily feed throughout pregnancy and consequently can rapidly translate high prey abundances into reproductive output through income breeding.

Influence of sex and reproductive condition on terrestrial and aquatic locomotor performance in the semi‐aquatic snake Seminatrix pygaea

1 Most life-history models assume a trade-off between reproductive investment and parental survival. Several studies have documented reproductive costs in terms of reduced locomotor performance in terrestrial habitats. However, few studies have determined the reproductive costs of pregnancy in aquatic environments, or compared pregnancy-induced locomotor costs among habitats. This knowledge gap is important because many organisms rely on multiple habitat types during pregnancy. 2 We compared sexual differences in maximum locomotor velocity and the relative impacts of pregnancy on locomotor performance in aquatic and terrestrial environments for a semi-aquatic snake (Seminatrix pygaea). In addition, because most life-history models predict a direct trade-off between reproductive investment and reproductive costs, we quantified the relationship between reproductive investment and postpartum increase in velocity for both habitat types. 3 Both males and non-pregnant females always swam faster than they crawled, but males were significantly faster for their size than were non-pregnant females. These results mirror sexual differences known to exist in other snakes, but differ in that the degree of sexual divergence in velocity does not vary with habitat for S. pygaea. 4 Pregnancy significantly reduced both crawling and swimming velocity. Moreover, pregnancy impaired crawling velocity significantly more than swimming velocity. The mean (± 1 SE) percentage increases in crawling and swimming velocity after parturition were 72·8 ± 21·6 and 59·4 ± 12·8%, respectively. There was a direct trade-off between reproductive investment and aquatic locomotor impairment: snakes that invested more in offspring experienced larger decreases in swimming velocity. However, evidence for such a trade-off in the terrestrial habitat was weaker. 5 Our results demonstrate that the cost of reproduction for semi-aquatic organisms may differ between aquatic and terrestrial habitats in complex ways. Swimming may be more effective than crawling for escaping predators during pregnancy, because swimming results in faster velocities and is less impaired by pregnancy. However, the assumption of a direct trade-off between reproductive investment and locomotor impairment may be stronger for swimming performance compared with crawling performance.

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). V. The temporal germ cell development strategy of the testis

AbstractThe germ cell development strategy during spermatogenesis was investigated in the black swamp snake (Seminatrix pygaea). Testicular tissues were collected, embedded in plastic, sectioned by ultramicrotome, and stained with methylene blue and basic fuchsin. Black swamp snakes have a postnuptial pattern of development, where spermatogenesis occurs from May to July and spermiation is completed by October. Though spatial relationships are seen between germ cells within the seminiferous epithelium during specific months, accumulation of spermatogonia and spermatocytes early in spermatogenesis and the depletion of spermatocytes and accumulation of spermatids late in spermatogenesis prevent consistent cellular associations. This temporal germ cell development within an amniotic testis is consistent with that seen in other recently studied temperate reptiles (slider turtle and wall lizard). These reptiles’ temporal development is more similar to the developmental strategy found in anamniotes than the spatial germ cell development that characterizes birds and mammals. Our findings also imply that a third germ cell development strategy may exist in temperate breeding reptiles. Because of the phylogenetic position of reptiles between anamniotes and other terrestrial amniotes, this common germ cell development strategy shared by temperate reptiles representing different orders may have significant implications as far as the evolution of sperm development within vertebrates.

Ultrastructural evidence for secretion from the epithelium of ampulla ductus deferentis of the fan‐throated lizard Sitana ponticeriana Cuvier

Among reptiles, an ampulla ductus deferentis has been reported only in Squamata. Fairly detailed studies are available only for two species, the lizard Calotes versicolor (Fam: Agamidae) and the snake Seminatrix pygaea (Fam: Colubridae). The light microscopic study on C. versicolor revealed the ampulla to be a prominent organ, whereas the light and transmission electron microscopic study in S. pygaea revealed it to be discernable only in histological preparations. Further, the epithelium of the ductal portion of vas deferens as well as the ampulla of C. versicolor appears to contribute to the seminal plasma and can also phagocytose dead sperm, whereas in S. pygaea neither of these roles has been established. Thus, we hypothesize that there may be variations in the anatomy, histology, and the role of the vas deferens in general, and the ampulla in particular, of the squamate reptiles. In this study, the ductus deferens of the small fan-throated lizard Sitana ponticeriana (Fam: Agamidae) was subjected to light and transmission electron microscopic analysis. In this lizard the ampulla is more prominent than in C. versicolor. The epithelium of the ductal portion of vas deferens consists of principal cells (with features reflecting roles in endocytosis and phagocytosis of dead sperm), dark cells (which are absent in the epithelium of the ductal portion of vas deferens of snakes), and basal cells. The ampulla of S. ponticeriana is differentiated into storage and glandular portions. The epithelium of the storage portion is like that in the ductal portion of the vas deferens, whereas that of the glandular portion, consisting of dark and light principal cells and foamy cells, is tall and forms into smooth villous folds. All three cell types show evidence for a role in secretion, in all likelihood different from each other, for release into the lumen to contribute to seminal plasma. These cells do not provide evidence of a role in phagocytosis of dead sperm. It appears that within the Squamata, the ductal ampulla differs in structure as well as function. We suggest that the ductal ampulla of agamid lizards is a composite gland of the ampulla ductus deferentis and seminal vesicles of mammals.

Unveiling Escape and Capture Rates of Aquatic Snakes and Salamanders (Siren spp. and Amphiuma means) in Commercial Funnel Traps

ABSTRACT Aquatic funnel trapping with commercially available minnow traps has proven effective for sampling several aquatic snake species. However, the efficacy of this technique for sampling snakes has received little controlled evaluation. We investigated the ability of aquatic snakes to escape from three funnel trap varieties (cylindrical steel, cylindrical plastic, and rectangular collapsible nylon mesh). We found that when intentionally released into traps, the majority (74%) of snakes escaped within 24 hours. Snakes escaped most frequently from collapsible traps, and of the species tested, Seminatrix pygaea escaped most frequently. We found significant differences in capture rates among trap types for S. pygaea, Farancia abacura (both captured most in plastic traps), and Nerodia fasciata (captured most in steel traps). Additionally, as we captured many large aquatic salamanders (Siren spp. and Amphiuma means), we also report trapping efficacies of the funnel traps for these amphibians.

Population Structure, Body Size, and Seasonal Activity of Black Swamp Snakes (Seminatrix pygaea)

We examined the ecology of a Black Swamp Snake (Seminatrix pygaea) population inhabiting an isolated wetland in the upper Coastal Plain of South Carolina. The observed population structure was skewed towards mature individuals, with neonates and juveniles underrepresented, perhaps due to trapping bias. The sex ratio was biased during May and June, with females outnumbering males, but no sex ratio bias was evident at other times of the year. Seminatrix pygaea showed sexual dimorphism in body size, with females being longer and heavier than males and males having relatively longer tails than females, but there was no difference in monthly growth rates. Approximately 76.3% of the mature females captured in May and June 1998 were pregnant. Therefore, most mature females in this population probably exhibit annual reproduction, while some undergo biennial reproduction. The majority of females gave birth in July or August, with a few births occurring in September and October, and perhaps even as early as May or June. Our mark-recapture estimates suggest a population density greater than 60 adult snakes per hectare, which indicates this small aquatic snake, endemic to the Southeast, may play a large role as both predator and prey within isolated wetland ecosystems.

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). IV. Occurrence of an ampulla ductus deferentis.

The distal end of the ductus deferens of Seminatrix pygaea (Cope) differs from more proximal portions of the tube by possessing a highly fluctuated epithelium. Similar morphology has been reported in this area in one lizard and some mammals and the region has been designated in these taxa as the ampulla ductus deferentis. In this study, light and transmission electron microscopy were used to study the posterior ductus deferens in S. pygaea and compare the histology in this region to more proximal regions of the duct and to descriptions of the ampulla of other species. Seminatrix pygaea stores sperm throughout the ductus deferens during the entire year. The epithelium of the ductus deferens is not secretory, but the presence of numerous small apical vesicles indicates a role in fluid absorption. In addition to the highly folded epithelium, clusters of sperm nuclei are more intimately associated with the apical ampullary epithelium than elsewhere in the ductus deferens. No evidence of phagocytosis of sperm was found. In contrast, the ampulla of mammals and presumably the lizard Calotes versicolor is glandular and phagocytic. The common character shared by the squamates and mammals with specializations in this area is the folded epithelium, and whether this is due to shared ancestry with amniotes or is homoplastic is unresolved.

Differential swimming performance of two natricine snakes exposed to a cholinesterase-inhibiting pesticide

Environmental contaminants have direct effects on organisms at the molecular, cellular, and tissue levels, but the net results of these sub-organismal effects are only consequential to exposed populations if they alter organism-level traits that ultimately influence fitness (e.g., growth, locomotor performance, reproduction, and survival). Here, we explore the possibility that the swimming performance of neonate black swamp snakes ( Seminatrix pygaea) and diamondback water snakes ( Nerodia rhombifer) may be affected by exposure to carbaryl (2.5 and 5.0 mg/L). The highest concentration of carbaryl caused greater reductions in swim velocity in S. pygaea than in N. rhombifer. Most individuals recovered from the effects of carbaryl on swimming performance within 96 h, but recovery was significantly slower in S. pygaea than in N. rhombifer. We hypothesize that the sensitivity of S. pygaea may arise from its highly permeable integument compared to other natricines. Our findings suggest that performance can serve as an ecologically relevant response to contaminant exposure in reptiles and warrants further study.

Assessing the Potential Impact of Cane Toads on Australian Snakes

Abstract: Cane toads (Bufo marinus) are large, highly toxic anurans that were introduced into Australia in 1937. Anecdotal reports suggest that the invasion of toads into an area is followed by dramatic declines in the abundance of terrestrial native frog‐eating predators, but quantitative studies have been restricted to nonpredator taxa or aquatic predators and have generally reported minimal impacts. Will toads substantially affect Australian snakes? Based on geographic distributions and dietary composition, we identified 49 snake taxa as potentially at risk from toads. The impact of these feral prey also depends on the snakes' ability to survive after ingesting toad toxins. Based on decrements in locomotor (swimming) performance after ingesting toxin, we estimate the LD50 of toad toxins for 10 of the at‐risk snake species. Most species exhibited a similar low ability to tolerate toad toxins. Based on head widths relative to sizes of toads, we calculate that 7 of the 10 taxa could easily ingest a fatal dose of toxin in a single meal. The exceptions were two colubrid taxa (keelbacks [ Tropidonophis mairii] and slatey‐grey snakes [ Stegonotus cucullatus]) with much higher resistance to toad toxins (up to 85‐fold) and one elapid (swamp snakes [ Hemiaspis signata]) with low resistance but a small relative head size and thus low maximum prey size. Overall, our analysis suggests that cane toads threaten populations of approximately 30% of terrestrial Australian snake species.

Ultrastructure of the reproductive system of the black swamp snake (seminatrix pygaea). III. Sexual segment of the male kidney

In mature male snakes and lizards, a distal portion of the nephron is hypertrophied in relation to its appearance in females and immature males. This sexual segment of the male kidney apparently provides seminal fluid that is mixed with sperm and released into the female cloaca during copulation. In this article, we provide the first study at the ultrastructural level of seasonal variation in the sexual segment of the kidney of a squamate, the natricine snake Seminatrix pygaea. Previous workers have indicated that the sexual segment is secretory only when the testes are spermatogenically active. The sexual segment of the kidney in S. pygaea does not go through an extended period of inactivity but does show a cycle of synthesis and secretion that can be related to the spermatogenic cycle and mating activity. We show that synthesis of secretory product is initiated with the onset of spermatogenic activity in the spring and culminates with completion of spermiation in the fall. Secretion of the product, however, occurs in a premating period in March when the testes are inactive. Secretion during this premating period is probably necessary to provide time for the passage of the products down the ureter in order to mix with sperm during mating later in spring.

Two cases of bites by the black-bellied swamp snake ( Hemiaspis signata)

We report two cases of envenomation by the black bellied swamp snake, Hemiaspis signata, with expert identification of the snakes. In the first case a 12 year old boy, who after the removal of the pressure immobilisation bandage, developed decreased fibrinogen levels and positive cross-linked fibrinogen degradation products (XDPs), but normal prothrombin time and activated partial prothrombin time. These changes resolved over 8 h with no treatment. In the second case a 7 year old boy had local pain, swelling and axillary lymphadenopathy following the bite. These cases indicate the potential for coagulopathy and local symptoms following bites by large specimens of H. signata in young children.